The general objective is to determine where and how estrogen acts in regulating gonadotropin secretion. Specific objectives are to determine (a) the effects of partial and complete hypothalamic deafferentation on gonadotropin and prolactin secretion in the ewe, (b) the concentration of estrogen receptor, gonadotropin releasing hormone (GnRH), catecholamines (CA), and the activity of enzymes which regulate CA metabolism (tyrosine hydroxylase dopamine-beta-hydroxylase, monoamine oxidase) in different regions of the hypothalamus, (c) the effects of hypothalamic deafferentation and estrogen treatment, alone and in combination, on levels of estrogen receptor, GnRH, CA, and enzyme activity in the hypothalamus,(d) the role of the preoptic region in estrogen-induced LH release in the ewe, and (e) changes which occur in the hypothalamus of the ewe during anestrus. Gonadotropins, prolactin, and GnRH will be assayed by radioimmunoassay. CAs and enzyme activities will be determined by radioenzymatic assays.